The present invention relates to a wind and wave energy plant, comprising a windmill with a rotor and a wave-actuated water pump that can drive a turbine whose output shaft is in driving connection with an electric generator.
U.S. Pat. No. 5,549,445 describes a seagoing platform for wind and wave energy extraction, in which a turbine chamber open downwards is encircled by an annular pontoon. Around the pontoon, a large number of wave-actuated pumps are arranged, driven by submerged driving means and sucking water out of the turbine chamber so that the water rises up through the chamber and thus passes an electric generator with associated turbine submerged in the chamber. Above the turbine an impeller wheel is moreover arranged in the chamber, driven directly by a vertical-axis windmill and thus also pumping water up through the chamber past the turbine. The water which passes this impeller wheel is discharged to the surroundings through openings in the upper part of the turbine chamber wall.
In plants for extraction of energy from wind and waves, the final price of the energy produced depends partly on the construction costs and partly on the overall efficiency. The known plants are generally rather complex and therefore expensive to construct, and moreover the efficiencies achieved are not optimum.
The object of the present invention is to provide a wind and wave energy plant of a more simple design and yielding a higher output than prior-art plants.
In view of this object, the plant is characterized in that the windmill includes a tubular mill tower, which is firmly anchored to the seabed and encloses a storage tank between the sea surface and the mill rotor, which tank can be filled with water by means of the pump via a non-return valve, and from which water can be led to the turbine.
In this way it is possible by means of one and the same member, namely a firmly anchored mill tower, to achieve a combination of two substantial advantages, namely better utilization of the wind energy, as the mill rotor is raised to a height with strong winds, and at the same time better utilization of the wave energy, as by pumping seawater into the mill tower and storing the water there it is possible to achieve such a large pressure drop across the turbine wheel that the efficiency of the turbine is substantially higher than in the prior-art plants, for example up to approximately 20%. Thus a greater energy production can be achieved without extra costly structural members, such as separate foundations for a windmill and a wave energy plant, or more, larger pumps.
Furthermore better quality of the power produced can be achieved as the number of revolutions of the turbine can be kept substantially constant regardless of the fact that the water flow from the wave-actuated pump may vary depending on the velocity of propagation and size of the waves. A varying water flow from the pump is equalized by a buffer effect caused by the stored water volume in the storage tank. The generator, which is driven by the turbine, can consequently supply power at a more uniform frequency and voltage, which is a substantial quality parameter.
In an advantageous embodiment, the storage tank is elongated and extends substantially from the area around the sea surface to the area at the rotor. In this way largely the entire length of the mill tower can be utilized for obtaining a large pressure drop across the turbine with consequent high efficiency and at the same time a large volume of stored water, which enables the turbine to operate particularly evenly.
In a structurally particularly advantageous embodiment, the mill tower is constituted by a slender pipe which in itself forms the wall of the storage tank, thereby saving materials for making a separate storage tank in the tower, the tower merely having to be closed at the bottom.
The turbine and the associated electric generator may advantageously be arranged in the mill tower under the storage tank. This allows the turbine inlet to be arranged in immediate continuation of the storage thank, thus achieving particularly favourable flow conditions at the inlet, which results in further improvement of the efficiency as well as uniform operation. This furthermore obviates the need for a separate housing for the turbine and the generator, and these components are particularly well protected against the weather in the mill tower, as, owing to its height, it must be of heavy dimensions. Thus, a particularly reliable function is made possible.
The pump and the non-return valve may also preferably be integral with the mill tower, thus providing short flow paths with consequently smaller losses and furthermore a simple and robust structure.
In a particularly compact embodiment, the mill tower has a foot section in which the turbine and the generator are arranged centrally in continuation of each other, and in which a cast foundation for the mill projects centrally in an upward direction, and the pump is a piston pump with one or more pistons capable of reciprocating in an area enclosing one or more of the members: turbine, generator or foundation. In this way the turbine inlet can be placed near the surface level of the sea, which renders possible a larger head of water over the turbine while the pistons of the pump can have a suitably long stroke, being arranged on a level with the turbine, the generator or the foundation in the direction of height of the mill tower. As the pump pistons are thus located peripherally in the mill tower immediately inside its outer wall, they can be connected in a simpler way with wave-actuated driving means located outside the tower.
In a preferred embodiment the pump piston or pistons may be moved by a wave-actuated elongated driving means, such as a float, which extends substantially in a diametrical direction in relation to the tower, and which is journalled rotatably around the longitudinal axis of the tower at the foot section of the tower. In this way the driving means can rotate in relation to the incoming waves depending on their direction of propagation so that the longitudinal axis of the driving means is substantially parallel with the wave crests, whereby substantially the largest part of the wave energy is transmitted to the driving means, which is influenced by an even upward force along its entire length. By journaling the driving means around the longitudinal axis of the tower, it can be connected in a simple and robust manner with pump pistons located inside the tower. Another advantage obtained is that the driving means is influenced by an extra water rise occurring through the deceleration of part of an incoming wave, as the latter hits the foot section of the mill tower and the foundation located below it.
The driving means may further be in the form of a float which in the area around the tower has a particularly large buoyancy volume allowing better utilization of the extra water rise mentioned above.
In an advantageous embodiment, the plant includes a sensor for recording the direction of propagation of the waves, and a control system for adjusting the driving means in relation to the recorded direction and by means of a preferably electric actuator, so that the longitudinal axis of the driving means is substantially parallel with the wave crests. This allows the orientation of the driving means to be optimized in relation to the direction of propagation of the waves so that the driving means is influenced by the largest possible upward force from the wave crests. Furthermore, the driving means then need not be formed so that it adjusts stably to the direction of the waves by itself; an area with a particularly large buoyancy volume may, for example, by means of the actuator, be held constantly at the side of the mill tower that faces the incoming waves.
The foundation of the tower may have a downwardly increasing diameter below the sea surface. This may cause enhancement of the extra water rise that occurs by deceleration of an incoming wave, as the foundation may form an upward ramp for the waves.
In one embodiment, the part of the external wall located at the sea surface is made of metal, and means for electrical heating of this part of the outer wall are included. In this way, ice can be melted which may otherwise in some cases inhibit the, function of the driving means or damage the tower if ice packing occurs.